4N HCl in 1,4-dioxane (5 mL, 20 mmol) was slowly added to a 0° C. solution of the above crude product (2R,3S)-2-(4-tert-Butoxycarbonylaminophenyl)-1-(2-methylbenzoyl)piperidine-3-carboxylic acid ethyl ester (840 mg, 1.72 mmol) in dry CH2Cl2 (4 mL). After the addition of the HCl, the reaction mixture was allowed to attain r.t and stirred for 1 h. It was diluted with CH2Cl2 (30 mL), cooled to 0° C. and neutralized with saturated aqueous NaHCO3 to get the (2R,3S)-2-(4-aminophenyl)-1-(2-methylbenzoyl)piperidine-3-carboxylic acid ethyl ester (612 mg) in 97% yield over two steps.
